1. Field of the Invention
The present invention relates to overhead hoist transport system; in particular, to overhead hoist wafer transport system.
2. Description of Related Art
Semi-conductor fabrication plant (fabs) usually own production tools to manufacture semi-conductor wafers, for example, processes such as exposure, etching, diffusing and ion implant, grinding through chemical machines or thin film deposition. During the process of manufacturing, the wafers will be transported to different production units (also known as BAY) to undergo corresponding manufacturing process, or remain in the same production unit to undergo different manufacturing process in different stages. Therefore, semi-conductor fabs usually make use of the auto-transportation system to assist in transporting the wafers to different production units throughout different stages of manufacturing.
Please refer to FIG. 1A, which shows a common arrangement of a conventional overhead hoist transport (OHT) system. The overhead track 1 usually comprise a main track 11 and a lateral track 12 furcated from the main track 11, forming a Y-shaped rail segment. A shuttle 2 travels on the aforementioned tracks to transport wafers, and the shuttle 2 has to go round the production tool 3″ in order to transport the wafers from tool 3 to tool 3′.
Additionally, as shown in FIG. 1B, in a semi-conductor fab, production tools are move-in/out very often to meet a new process or product need, or in cases where more production tools are needed due to the increase of production, thus the position of the track 1, the OHT rail of the prior art, and the production tool have resulted a waste in space in the clean room, hence the clean room are expanded to meet the needs, likewise increasing the cost.
If the OHT rail in FIG. 1B is replaced by the OHT rail in FIG. 1C, one more production tool may fit in the very limited clean room space, but the shuttle 2 will have to travel a longer distance whenever the shuttle 2 transports the wafers from tool 4 to tool 4′, hence wasting more time in traveling during production stages, resulting a lower transfer efficiency.
Due to these reasons, the inventors believe these defects can be improved, and through research and application of the academic studies, eventually a design is proposed which effectively modifies the aforementioned defects.